Aqueous-Based Insulating Fluids and Related Methods

ABSTRACT

Provided herein are methods and compositions that include a method comprising providing an annulus between a first tubing and a second tubing; providing an aqueous-based insulating fluid that comprises an aqueous base fluid, a water-miscible organic liquid, and a layered silicate; and placing the aqueous-based insulating fluid in the annulus. A composition provided includes an aqueous-based insulating fluid comprising an aqueous base fluid, a water-miscible organic liquid, and a layered silicate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 11/685,909 entitled “Improved Aqueous-Based Insulating Fluidsand Related Methods,” filed on Mar. 14, 2007, the entirety of which isherein incorporated by reference, and from which priority is claimedpursuant to 35 U.S.C. §120.

BACKGROUND

The present invention relates to insulating fluids, and moreparticularly, to aqueous-based insulating fluids that have greaterstability at high temperatures with lower thermal conductivity that maybe used, for example, in applications requiring an insulating fluid suchas pipeline and subterranean applications (e.g., to insulate petroleumproduction conduits).

Insulating fluids are often used in subterranean operations wherein thefluid is placed into an annulus between a first tubing and a secondtubing or the walls of a well bore. The insulating fluid acts toinsulate a first fluid (e.g., a hydrocarbon fluid) that may be locatedwithin the first tubing from the environment surrounding the firsttubing or the second tubing to enable optimum recovery of thehydrocarbon fluid. For instance, if the surrounding environment is verycold, the insulating fluid is thought to protect the first fluid in thefirst tubing from the environment so that it can efficiently flowthrough the production tubing, e.g., the first tubing, to otherfacilities. This is desirable because heat transfer can cause problemssuch as the precipitation of heavier hydrocarbons, severe reductions inflow rate, and in some cases, casing collapse. Additionally, when usedin packer applications, a required amount of hydrostatic head pressureis needed. Thus, higher density insulating fluids are often used forthis reason as well to provide the requisite hydrostatic force.

Such fluids also may be used for similar applications involvingpipelines for similar purposes, e.g., to protect a fluid located withinthe pipeline from the surrounding environmental conditions so that thefluid can efficiently flow through the pipeline. Insulating fluids canbe used in other insulating applications as well wherein it is desirableto control heat transfer. These applications may or may not involvehydrocarbons.

Beneficial insulating fluids preferably have a low inherent thermalconductivity, and also should remain gelled to prevent, inter alia,convection currents that could carry heat away. Additionally, preferredinsulating fluids should be aqueous-based, and easy to handle and use.Moreover, preferred fluids should tolerate ultra high temperatures(e.g., temperatures of 400° F. or above) for long periods of time foroptimum performance.

Conventional aqueous-based insulating fluids have been subject to manydrawbacks. First, many have associated temperature limitations.Typically, most aqueous-based insulating fluids are only stable up to240° F. for relatively short periods of time. This can be problematicbecause it can result in premature degradation of the fluid, which cancause the fluid not to perform its desired function with respect toinsulating the first fluid. A second common limitation of manyconventional aqueous-based insulating fluids is their density range.Typically, these fluids have an upper density limit of 12.5 ppg.Oftentimes, higher densities are desirable to maintain adequate pressurefor the chosen application. Additionally, most aqueous-based insulatingfluids have excessive thermal conductivities, which means that thesefluids are not as efficient or effective at controlling conductive heattransfer. Moreover, when a viscosified fluid is required to eliminateconvective currents, oftentimes to obtain the required viscosity incurrent aqueous-based fluids, the fluids may become too thick to be ableto pump into place. Some aqueous-based fluids also can have differentsalt tolerances that may not be compatible with various brines used,which limits the operators' options as to what fluids to use in certaincircumstances.

In some instances, insulating fluids may be oil-based. Certain oil-basedfluids may offer an advantage because they may have lower thermalconductivity as compared to their aqueous counterparts. However, manydisadvantages are associated with these fluids as well. First, oil-basedinsulating fluids can be hard to “weight up,” meaning that it may behard to obtain the necessary density required for an application.Secondly, oil-based fluids may present toxicity and other environmentalissues that must be managed, especially when such fluids are used insub-sea applications. Additionally, there can be interface issues ifaqueous completion fluids are used. Another complication presented whenusing oil-based insulating fluids is the concern about theircompatibility with any elastomeric seals that may be present along thefirst tubing line.

Another method that may be employed to insulate a first tubing involvesusing vacuum insulated tubing. However, this method also can presentdisadvantages. First, when the vacuum tubing is installed on acompletion string, sections of the vacuum tubing can fail. This can be acostly problem involving a lot of down time. In severe cases, the firsttubing can collapse. Secondly, vacuum insulated tubing can be verycostly and hard to place. Moreover, in many instances, heat transfer atthe junctions or connective joints in the vacuum tubings can beproblematic. These may lead to “hot spots” in the tubings.

SUMMARY

The present invention relates to insulating fluids, and moreparticularly, to aqueous-based insulating fluids that have greaterstability at high temperatures with lower thermal conductivity that maybe used, for example, in applications requiring an insulating fluid suchas pipeline and subterranean applications (e.g., to insulate petroleumproduction conduits).

In one embodiment, the present invention provides a method comprising:providing an annulus between a first tubing and a second tubing;providing an aqueous-based insulating fluid that comprises an aqueousbase fluid, a water-miscible organic liquid, and a layered silicate; andplacing the aqueous-based insulating fluid in the annulus. In someembodiments, the aqueous-based insulating fluid also includes a polymer.

In one embodiment, the present invention provides a method comprising:providing a tubing containing a first fluid located within a well boresuch that an annulus is formed between the tubing and a surface of thewell bore; providing an aqueous-based insulating fluid that comprises anaqueous base fluid, a water-miscible organic liquid, and a layeredsilicate; and placing the aqueous-based insulating fluid in the annulus.In some embodiments, the aqueous-based insulating fluid also includes apolymer.

In one embodiment, the present invention provides a method comprising:providing a first tubing that comprises at least a portion of a pipelinethat contains a first fluid; providing a second tubing thatsubstantially surrounds the first tubing thus creating an annulusbetween the first tubing and the second tubing; providing anaqueous-based insulating fluid that comprises an aqueous base fluid, awater-miscible organic liquid, and a layered silicate; and placing theaqueous-based insulating fluid in the annulus. In some embodiments, theaqueous-based insulating fluid also includes a polymer.

In one embodiment, the present invention provides an aqueous-basedinsulating fluid that comprises an aqueous base fluid, a water-miscibleorganic liquid, and a layered silicate. In some embodiments, theaqueous-based insulating fluid also includes a polymer.

In another embodiment, the present invention provides a method offorming an aqueous-based insulating fluid comprising: mixing an aqueousbase fluid and a water-miscible organic liquid to form a mixture; addingat least one layered silicate to the mixture; allowing the silicate tohydrate; placing the mixture comprising the layered silicate in a chosenlocation; allowing the mixture comprising the layered silicate toactivate to form a gel therein. In some embodiments, a polymer may beadded to the mixture and allowed to hydrate. Optionally, a crosslinkingagent may be added to the mixture comprising the polymer to crosslinkthe polymer.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present invention, and should not be used to limit or define theinvention.

FIG. 1 lists the materials used in the formulations and the amountsthereof as described in Example 1 in the Examples section.

FIG. 2 illustrates data from a fluid that was heated to about 190° F.for 5000 minutes to activate the crosslinking agent and provide anincrease in viscosity.

FIG. 3 lists the materials that may be used in the formulations and theapproximate amounts thereof as described in Example 2 in the Examplessection.

FIG. 4 illustrates data from a fluid that was heated from approximately100° F. to approximately 600° F. for approximately 45,000 seconds atapproximately 10,000 psi.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to insulating fluids, and moreparticularly, to aqueous-based insulating fluids that have greaterstability at high temperatures with lower thermal conductivity that maybe used, for example, in applications requiring an insulating fluid suchas pipeline and subterranean applications (e.g., to insulate petroleumproduction conduits). The aqueous-based insulating fluids of the presentinvention may be used in any application requiring an insulating fluid.Preferably, they may be used in pipeline and subterranean applications.

The improved aqueous-based insulating fluids and methods of the presentinvention present many potential advantages, only some of which arealluded to herein. One of these many advantages is that the fluids mayhave enhanced thermal stability, which enables them to be beneficiallyused in many applications. Secondly, in some embodiments, theaqueous-based insulating fluids of the present invention may have higherdensities than conventional aqueous-based insulating fluids, andtherefore, present a distinct advantage in that respect. Additionally,the aqueous-based insulating fluids of the present invention haverelatively low thermal conductivity, which is thought to be especiallybeneficial in certain applications. In some embodiments, these fluidsare believed to be very durable. Moreover, in some embodiments, thefluids of the present invention offer aqueous-based viscous insulatingfluids with a broad fluid density range, decreased thermal conductivity,and stable gel properties at temperatures exceeding those of currentindustry standards (e.g., even at temperatures of about 600° F. or more,depending on the organic liquid included). Another potential advantageis that these fluids may prevent the formation of hydrates within theinsulating fluids themselves or the fluids being insulated. Otheradvantages and objects of the invention may be apparent to one skilledin the art with the benefit of this disclosure.

In certain embodiments, the aqueous-based insulating fluids of thepresent invention comprise an aqueous base fluid, a water-miscibleorganic liquid, and a layered silicate. In certain embodiments, theaqueous-based insulating fluids of the present invention comprise anaqueous base fluid, a water-miscible organic liquid, a layered silicate,and optionally a synthetic polymer. In some instances, the polymer maybe crosslinked by using or adding to the fluid an appropriatecrosslinking agent. Thus, the term “polymer” as used herein refers tooligomers, copolymers, terpolymers and the like, which may or may not becrosslinked. Optionally, the aqueous-based insulating fluids of thepresent invention may comprise other additives such as corrosioninhibitors, pH modifiers, biocides, glass beads, hollow spheres (e.g.,hollow microspheres), rheology modifiers, buffers, hydrate inhibitors,breakers, tracers, additional weighting agents, viscosifiers,surfactants, and combinations of any of these. Other additives may beappropriate as well and beneficially used in conjunction with theaqueous-based insulating fluids of the present invention as may berecognized by one skilled in the art with the benefit of thisdisclosure.

The aqueous base fluids that may be used in the aqueous-based insulatingfluids of the present invention include any aqueous fluid suitable foruse in insulating, subterranean, or pipeline applications. In someinstances, brines may be used, for example, when a relatively denseraqueous-based insulating fluid is desired (e.g., density of 10.5 ppg orgreater); however, it may be observed that the fluids of the presentinvention may be less tolerant to higher concentrations of salts thanother fluids, such as those that include a polymer as described hereinbut not a layered silicate as described herein. Suitable brines include,but are not limited to: NaCl, NaBr, KCl, CaCl₂, CaBr₂, ZrBr₂, sodiumcarbonate, sodium formate, potassium formate, cesium formate, andcombinations and derivatives of these brines. Others may be appropriateas well. The specific brine used may be dictated by the desired densityof the resulting aqueous-based insulating fluid or for compatibilitywith other completion fluid brines that may be present. Denser brinesmay be useful in some instances. A density that is suitable for theapplication at issue should be used as recognized by one skilled in theart with the benefit of this disclosure. When deciding how much of anaqueous fluid to include, a general guideline to follow is that theaqueous fluid component should comprise the balance of a hightemperature aqueous-based insulating fluid after considering the amountof the other components present therein.

The water-miscible organic liquids that may be included in theaqueous-based insulating fluids of the present invention includewater-miscible materials having relatively low thermal conductivity(e.g., about half as conductive as water or less). By “water-miscible,”it is meant that about 5 grams or more of the organic liquid willdisperse in 100 grams of water. Suitable water-miscible organic liquidsinclude, but are not limited to, esters, amines, alcohols, polyols,glycol ethers, or combinations and derivatives of these. Examples ofsuitable esters include low molecular weight esters; specific examplesinclude, but are not limited to, methylformate, methyl acetate, andethyl acetate. Combinations and derivatives are also suitable. Examplesof suitable amines include low molecular weight amines; specificexamples include, but are not limited to, diethyl amine, 2-aminoethanol,and 2-(dimethylamino)ethanol. Combinations and derivatives are alsosuitable. Examples of suitable alcohols include methanol, ethanol,propanol, isopropanol, and the like. Combinations and derivatives arealso suitable. Examples of glycol ethers include ethylene glycol butylether, diethylene glycol methyl ether, dipropylene glycol methyl ether,tripropylene glycol methyl ether, and the like. Combinations andderivatives are also suitable. Of these, polyols are generally preferredin most cases over the other liquids since they generally are thought toexhibit greater thermal and chemical stability, higher flash pointvalues, and are more benign with respect to elastomeric materials.

Suitable polyols are those aliphatic alcohols containing two or morehydroxy groups. It is preferred that the polyol be at least partiallywater-miscible. Examples of suitable polyols that may be used in theaqueous-based insulating fluids of this invention include, but are notlimited to, water-soluble diols such as ethylene glycols, propyleneglycols, polyethylene glycols, polypropylene glycols, diethyleneglycols, triethylene glycols, dipropylene glycols and tripropyleneglycols, combinations of these glycols, their derivatives, and reactionproducts formed by reacting ethylene and propylene oxide or polyethyleneglycols and polypropylene glycols with active hydrogen base compounds(e.g., polyalcohols, polycarboxylic acids, polyamines, or polyphenols).The polyglycols of ethylene generally are thought to be water-miscibleat molecular weights at least as high as 20,000. The polyglycols ofpropylene, although giving slightly better grinding efficiency than theethylene glycols, are thought to be water-miscible up to molecularweights of only about 1,000. Other glycols possibly contemplated includeneopentyl glycol, pentanediols, butanediols, and such unsaturated diolsas butyne diols and butene diols. In addition to the diols, the triol,glycerol, and such derivatives as ethylene or propylene oxide adductsmay be used. Other higher polyols may include pentaerythritol. Anotherclass of polyhydroxy alcohols contemplated is the sugar alcohols. Thesugar alcohols are obtained by reduction of carbohydrates and differgreatly from the above-mentioned polyols. Combinations and derivativesof these are suitable as well.

The choice of polyol to be used is largely dependent on the desireddensity of the fluid. Other factors to consider include thermalconductivity. For higher density fluids (e.g., 10.5 ppg or higher), ahigher density polyol may be preferred, for instance, triethylene glycolor glycerol may be desirable in some instances. For lower densityapplications, ethylene or propylene glycol may be used. In someinstances, more salt may be necessary to adequately weight the fluid tothe desired density. In certain embodiments, the amount of polyol thatshould be used may be governed by the thermal conductivity ceiling ofthe fluid and the desired density of the fluid. If the thermalconductivity ceiling is 0.17 BTU/hft° F., then the concentration of thepolyol may be from about 40% to about 99% of a high temperatureaqueous-based insulating fluid of the present invention. A morepreferred range could be from about 70% to about 99%.

Examples of layered silicates that may be suitable for use in thepresent invention include, but are not limited to, smectite,vermiculite, swellable fluoromica, montmorillonite, beidellite,hectorite, and saponite. A high-temperature, electrolyte stablesynthetic hectorite may be particularly useful in some embodiments. Anexample of a synthetic hectorite clay for use in accordance with thisinvention is “LAPONITE™ RD” commercially available from LaporteAbsorbents Company of Cheshire, United Kingdom. Mixtures of any of theseof silicates may be suitable as well. In preferred embodiments, thesilicate may be at least partially water soluble. In some embodiments,the layered silicate may be a natural layered silicate or a syntheticlayered silicate. In certain embodiments, the silicate should comprisefrom about 0.1% to about 15% weight by volume of the fluid, and morepreferably, from about 0.5% to about 4% weight by volume of the fluid.

Inclusion of a synthetic polymer may be useful, inter alia, to producefluids that exhibit gelation behavior. Examples of synthetic polymersthat optionally may be suitable for use in the present inventioninclude, but are not limited to, acrylic acid polymers, acrylic acidester polymers, acrylic acid derivative polymers, acrylic acidhomopolymers, acrylic acid ester homopolymers (such as poly(methylacrylate), poly (butyl acrylate), and poly(2-ethylhexyl acrylate)),acrylic acid ester co-polymers, methacrylic acid derivative polymers,methacrylic acid homopolymers, methacrylic acid ester homopolymers (suchas poly(methyl methacrylate), polyacrylamide homopolymer, n-vinylpyrrolidone and polyacrylamide copolymers, poly(butyl methacrylate), andpoly(2-ethylhexyl methacrylate)), n-vinyl pyrrolidone,acrylamido-methyl-propane sulfonate polymers, acrylamido-methyl-propanesulfonate derivative polymers, acrylamido-methyl-propane sulfonateco-polymers, and acrylic acidlacrylamido-methyl-propane sulfonatecopolymers, and combinations thereof. Copolymers and terpolymers may besuitable as well. Mixtures of any of these of polymers may be suitableas well. In preferred embodiments, the polymer should be at leastpartially water soluble. Suitable polymers can be cationic, anionic,nonionic, or zwitterionic. In certain embodiments, the polymer shouldcomprise from about 0.1% to about 15% weight by volume of the fluid, andmore preferably, from about 0.5% to about 4%.

To obtain the desired gel characteristics and thermal stability for anaqueous-based insulating fluid of the present invention, the polymerincluded in the fluid may be crosslinked by an appropriate crosslinkingagent. In those embodiments of the present invention wherein it isdesirable to crosslink the polymer, optionally and preferably, one ormore crosslinking agents may be added to the fluid to crosslink thepolymer.

One type of suitable crosslinking agent is a combination of a phenoliccomponent (or a phenolic precursor) and formaldehyde (or formaldehydeprecursor). Suitable phenolic components or phenolic precursors include,but are not limited to, phenols, hydroquinone, salicylic acid,salicylamide, aspirin, methyl-p-hydroxybenzoate, phenyl acetate, phenylsalicylate, o-aminobenzoic acid, p-aminobenzoic acid, m-aminophenol,furfuryl alcohol, and benzoic acid. Suitable formaldehyde precursors mayinclude, but are not limited to, hexamethylenetetramine, glyoxal, and1,3,5-trioxane. This crosslinking agent system needs approximately 250°F. to thermally activate to crosslink the polymer. Another type ofsuitable crosslinking agent is polyalkylimine. This crosslinking agentneeds approximately 90° F. to activate to crosslink the polymer. Thiscrosslinking agent may be used alone or in conjunction with any of theother crosslinking agents discussed herein.

Another type of crosslinking agent that may be used includes non-toxicorganic crosslinking agents that are free from metal ions. Examples ofsuch organic cross-linking agents are polyalkyleneimines (e.g.,polyethyleneimine), polyalkylenepolyamines and mixtures thereof. Inaddition, water-soluble polyfunctional aliphatic amines, arylalkylaminesand heteroarylalkylamines may be utilized.

When included, suitable crosslinking agents may be present in the fluidsof the present invention in an amount sufficient to provide, inter alia,the desired degree of crosslinking. In certain embodiments, thecrosslinking agent or agents may be present in the fluids of the presentinvention in an amount in the range of from about 0.0005% to about 10%weight by volume of the fluid. In certain embodiments, the crosslinkingagent may be present in the fluids of the present invention in an amountin the range of from about 0.001% to about 5% weight by volume of thefluid. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of crosslinking agentto include in a fluid of the present invention based on, among otherthings, the temperature conditions of a particular application, the typeof polymer(s) used, the molecular weight of the polymer(s), the desireddegree of viscosification, and/or the pH of the fluid.

Although any suitable method for forming the insulating fluids of thepresent invention may be used, in some embodiments, an aqueous-basedinsulating fluid of the present invention may be formulated at ambienttemperature and pressure conditions by mixing water and a chosenwater-miscible organic liquid. The water and water-miscible organicliquid preferably may be mixed so that the water-miscible organic liquidis miscible in the water. The chosen silicate may then be added andmixed into the water and water-miscible organic liquid mixture until thesilicate is hydrated. Any chosen additives may be added at any,including a polymer. Preferably, any additives are dispersed within themixture. If desired, a crosslinking agent may be added. If used, itshould be dispersed in the mixture. Crosslinking, however, generallyshould not take place until thermal activation, which preferably, insubterranean applications, occurs downhole; this may alleviate anypumping difficulties that might arise as a result of activation beforeplacement. Activation results in the fluid forming a gel. The term“gel,” as used herein, and its derivatives refer to a semi-solid,jelly-like state assumed by some colloidal dispersions. Once activated,the gel should stay in place and be durable with negligible syneresis.

In some embodiments, the gels formed by hydrating the silicate may havea zero sheer viscosity of about 100,000 centipoise measured on an AntonPaar Controlled Stress Rheometer at standard conditions using standardoperating procedure.

Once gelled, if the fluid contains polymer, one method of removing thegel may comprise diluting or breaking the crosslinks and/or the polymerstructure within the gel using an appropriate method and/or compositionto allow recovery or removal of the gel. Another method could involvephysical removal of the gel by, for example, air or liquid.

In some embodiments, the aqueous-based insulating fluids of the presentinvention may be prepared on-the-fly at a well-site or pipelinelocation. In other embodiments, the aqueous-based insulating fluids ofthe present invention may be prepared off-site and transported to thesite of use. In transporting the fluids, one should be mindful of theactivation temperature of the fluid.

In one embodiment, the present invention provides a method comprising:providing a first tubing; providing a second tubing that substantiallysurrounds the first tubing thus creating an annulus between the firsttubing and the second tubing; providing an aqueous-based insulatingfluid that comprises an aqueous base fluid, a polyol, and a layeredsilicate; and placing the aqueous-based insulating fluid in the annulus.In some embodiments, the aqueous-based insulating fluid also includes apolymer. The tubings may have any shape appropriate for a chosenapplication. In some instances, the second tubing may not be the samelength as the first tubing. In some instances, the tubing may comprise aportion of a larger apparatus. In some instances, the aqueous-basedinsulating fluid may be in contact with the entire first tubing from endto end, but in other situations, the aqueous-based insulating fluid mayonly be placed in a portion of the annulus and thus only contact aportion of the first tubing. In some instances, the first tubing may beproduction tubing located within a well bore. In some instances, thetubings may be located in a geothermal well bore. The production tubingmay be located in an off-shore location. In other instances, theproduction tubing may be located in a cold climate. In other instances,the first tubing may be a pipeline capable of transporting a fluid fromone location to a second location.

In one embodiment, the present invention provides a method comprising:providing a first tubing; providing a second tubing that substantiallysurrounds the first tubing thus creating an annulus between the firsttubing and the second tubing; providing an aqueous-based insulatingfluid that comprises an aqueous base fluid, a water-miscible organicliquid, and a layered silicate; and placing the aqueous-based insulatingfluid in the annulus. In some embodiments, the aqueous-based insulatingfluid also includes a polymer.

In one embodiment, the present invention provides a method comprising:providing a tubing containing a first fluid located within a well boresuch that an annulus is formed between the tubing and a surface of thewell bore; providing an aqueous-based insulating fluid that comprises anaqueous base fluid, a water-miscible organic liquid, and a layeredsilicate; and placing the aqueous-based insulating fluid in the annulus.In some embodiments, the aqueous-based insulating fluid also includes apolymer.

In one embodiment, the present invention provides a method comprising:providing a first tubing that comprises at least a portion of a pipelinethat contains a first fluid; providing a second tubing thatsubstantially surrounds the first tubing thus creating an annulusbetween the first tubing and the second tubing; providing anaqueous-based insulating fluid that comprises an aqueous base fluid, awater-miscible organic liquid, and a layered silicate; and placing theaqueous-based insulating fluid in the annulus. In some embodiments, theaqueous-based insulating fluid also includes a polymer.

In one embodiment, the present invention provides an aqueous-basedinsulating fluid that comprises an aqueous base fluid, a water-miscibleorganic liquid, and a layered silicate. In some embodiments, theaqueous-based insulating fluid also includes a polymer.

In another embodiment, the present invention provides a method offorming an aqueous-based insulating fluid comprising: mixing an aqueousbase fluid and a water-miscible organic liquid to form a mixture; addingat least one layered silicate to the mixture; allowing the layeredsilicate to hydrate; placing the mixture comprising the layered silicatein a chosen location; allowing the mixture comprising the layeredsilicate to activate to form a gel therein. In some embodiments, apolymer may be added to the mixture and allowed to hydrate. Optionally,a crosslinking agent may be added to the mixture comprising the polymerto crosslink the polymer.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the invention.

EXAMPLES [[[Ryan—Confirm that These Examples were Performed Exactly asWritten Below.]]] Example 1

We studied the formulation and testing of various combinations ofinorganic, organic, clay and polymeric materials for use asviscosifying/gelling agents in aqueous based fluids for insulatingfluids. We conducted a series of tests in which the solubility, thermalconductivity, thermal stability, pH, gelling properties, Theologicalbehavior, and toxicity of the various fluids were evaluated andcompared. Perhaps most importantly, the thermal stability ranges from37° F. to 280° F. and above were evaluated. These tests were conductedover short and long term periods. FIG. 1 lists the materials used in theformulations and the amounts tested. This in no way should be construedas an exhaustive example with reference to the invention or as adefinition of the invention in any way.

Thermal stability and static aging: All formulations of fluids werestatically aged at temperatures≧about 280° F. for two months.Formulations and properties for the tested fluids are shown in Tables 1and 2 below. Most of the fluids appeared to remain intact, with thecrosslinked systems showing an increase in viscosity and what appearedto be complete gelation behavior. We believe that these systems appearedto exhibit more desirable stability properties than other fluids, whichincluded numerous biopolymers (e.g., xanthan, welan, and diutan gums)and inorganic clays and were generally destroyed after 3 days at 250° F.In addition, as to the thermal stability of these formulations tested,less than 1% syneresis was observed for any of the samples.

In addition to the static tests, Sample 4 was evaluated using ahigh-temperature viscometer to examine the thermal activation ofcrosslinking agents (FIG. 2). The fluid was subjected to a low shearrate at 190° F., with viscosity measurements showing an increase withtime to reach the maximum recordable level around 5000 minutes.

TABLE 1 IPF Formulations and Properties Before Static Aging. Sample 1 23 4 Formulations Density, ppg 8.5 10.5 12.3 11.3 Water, % vol 20 10 — 1Glycerol, % vol — 90 78.5 90 PG, % vol 80 — — — Brine, % vol — — 21.5 9Polymer A, % wt 1 1 1 — Polymer B, % wt — — — 1.25 Aldehyde, ppm 50005000 5000 — HQ, ppm 5000 5000 5000 — PEI, % wt — — — 2 Properties 300rpm¹ 280 285 270 82 Shear Strength, lb/100 ft² 13.4 20.65 20.65 >13.4Thermal Conductivity², 0.141 0.172 0.154 0.158 BTU/hftF ¹Measurementsobtained from reading observed on Fann 35 viscometer, sample temperature120° F. ²Measurements obtained by KD2-Pro Thermal Properties Analyzer.

TABLE 2 IPF Formulations and Properties After 60 Days Static Aging at280° F. Sample 1 2 3 4 Formulations Density, ppg 8.5 10.5 12.3 11.3Water, % vol 20 10 — 1 Glycerol, % vol — 90 78.5 90 PG, % vol 80 — — —Brine, % vol — — 21.5 9 Polymer A, % wt 1 1 1 — Polymer B, % wt — — —1.25 Aldehyde, ppm 5000 5000 5000 — HQ, ppm 5000 5000 5000 — PEI, % wt —— — 2 Properties 300 rpm³ max max max max Shear Strength, lb/100ft² >50 >50 >50 >50 Thermal Conductivity, 0.141 0.172 0.154 0.158BTU/hftF ³Fluids gelled, off-scale measurement.

Thermal conductivity measurements: The importance of a low thermalconductivity (K) is an important aspect of the success of insulatingfluids. For effective reduction of heat transfer, aqueous-based packerfluids in the density range of 8.5 to 12.3 ppg are expected to exhibitvalues for K of 0.3 to 0.2 BTU/hr ft ° F., and preferably would havelower values. From the various formulations listed above, using theseformulations fluid densities of 8.5 to 14.4 ppg were observed, all ofwhich have a thermal conductivity of <0.2 BTU/hr ft ° F. as shown inTables 1 and 2.

Example 2

We studied the formulation and testing of various combinations ofinorganic, organic, clay and polymeric materials for use asviscosifying/gelling agents in aqueous based fluids for insulatingfluids. We conducted a series of tests in which the solubility, thermalconductivity, thermal stability, pH, gelling properties, Theologicalbehavior, and toxicity of the various fluids were evaluated andcompared. Perhaps most importantly, the thermal stability ranges from37° F. to 500° F. and above were evaluated. These tests were conductedover short and long term periods. FIG. 3 lists the materials used in theformulations and the amounts tested. This in no way should be construedas an exhaustive example with reference to the invention or as adefinition of the invention in any way.

Thermal stability and static aging: All formulations of fluids werestatically aged at temperatures≧about 400° F. for 3 day intervals.Formulations and properties for the tested fluids are shown in Tables 3and 4 below. Most of the fluids appeared to remain intact, with thecrosslinked systems showing an increase in viscosity and what appearedto be complete gelation behavior. We believe that these systems appearedto exhibit more desirable stability properties than other fluids, whichincluded numerous biopolymers (e.g., xanthan, welan, and diutan gums)and inorganic clays and were generally destroyed after 3 days at 250° F.In addition, as to the thermal stability of these formulations tested,less than 1% syneresis was observed for any of the samples.

TABLE 3 IPF Formulations and Properties Before Static Aging Sample 1 2Thermal conductivity, BTU/(hft ° F.) 0.166 0.177 Density, lb/gal 10.59.5 Fann ® 35 Viscometer, 150° F. 150° F. 600 rpm 160 161 300 rpm 125126 200 rpm 109 102 100 rpm 84 88  6 rpm 37 40  3 rpm 34 38 PV 35 35 YP90 91

TABLE 4 IPF Formulations and Properties After 72 Hours Static Aging at450° F. Sample 1 2 Thermal conductivity, BTU/(hft ° F.) 0.166 0.177Density, lb/gal 10.5 9.5 Fann ® 35 Viscometer, 150° F. 150° F. 600 rpm163 159 300 rpm 127 122 200 rpm 111 104 100 rpm 82 86  6 rpm 40 41  3rpm 36 37 PV 36 35 YP 91 85

Thermal conductivity measurements: The importance of a low thermalconductivity (K) is an important aspect of the success of insulatingfluids. For effective reduction of heat transfer, aqueous-based packerfluids in the density range of 8.5 to 10.5 ppg are expected to exhibitvalues for K of 0.3 to 0.2 BTU/hr ft ° F., and preferably would havelower values. From the various formulations listed above, using theseformulations fluid densities of 8.5 to 10.5 ppg were observed, all ofwhich have a thermal conductivity of <0.2 BTU/hr ft ° F. as shown inTables 3 and 4.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. All numbers and ranges disclosed abovemay vary by any amount (e.g., 1 percent, 2 percent, 5 percent, or,sometimes, 10 to 20 percent). Whenever a numerical range, R, with alower limit, RL, and an upper limit, RU, is disclosed, any numberfalling within the range is specifically disclosed. In particular, thefollowing numbers within the range are specifically disclosed:R=RL+k*(RU−RL), wherein k is a variable ranging from 1 percent to 100percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99percent, or 100 percent. Moreover, any numerical range defined by two Rnumbers as defined in the above is also specifically disclosed.Moreover, the indefinite articles “a” or “an”, as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.

1. A method comprising: providing an annulus between a first tubing anda second tubing; providing an aqueous-based insulating fluid thatcomprises an aqueous base fluid, a water-miscible organic liquid, and alayered silicate; and placing the aqueous-based insulating fluid in theannulus.
 2. The method of claim 1 wherein the aqueous-based insulatingfluid further comprises a polymer.
 3. The method of claim 1 wherein theaqueous-based insulating fluid further comprises at least one additiveselected from the group consisting of: a corrosion inhibitor, a pHmodifier, a biocide, a glass bead, a hollow sphere, a hollowmicrosphere, a rheology modifier, a buffer, a hydrate inhibitor, abreaker, a tracer, an additional weighting agent, a viscosifier, and asurfactant.
 4. The method of claim 1 wherein the aqueous base fluidcomprises at least one brine selected from the group consisting of:NaCl, NaBr, KCl, CaCl₂, CaBr₂, ZrBr₂, sodium carbonate, sodium formate,potassium formate, and cesium formate, and a derivative thereof.
 5. Themethod of claim 1 wherein the water-miscible organic liquid comprises atleast one liquid selected from the group consisting of: an ester, anamine, an alcohol, a polyol, a glycol ether, and a derivative thereof.6. The method of claim 5 wherein the polyol comprises at least onepolyol selected from the group consisting of: a water-soluble diol;ethylene glycol; propylene glycol; polyethylene glycol; polypropyleneglycol; diethylene glycol; triethylene glycol; dipropylene glycol;tripropylene glycol; a reaction product formed by reacting ethylene andpropylene oxide with an active hydrogen base compound; a reactionproduct formed by reacting polyethylene glycol and polypropylene glycolwith an active hydrogen base compound; neopentyl glycol; a pentanediol;a butanediol; an unsaturated diol; a butyne diol; a butene diol; atriol; glycerol; an ethylene adduct, a propylene oxide adduct;pentaerythritol; a sugar alcohol; and a derivative thereof.
 7. Themethod of claim 1 wherein the layered silicate comprises at least onelayered silicate selected from the group consisting of: smectite,vermiculite, swellable fluoromica, montmorillonite, beidellite,hectorite, and saponite.
 8. The method of claim 7 wherein the layeredsilicate is a synthetic layered silicate.
 9. The method of claim 7wherein the layered silicate is present in the fluid in an amount in therange of from about 0.1% to about 15% by weight of the fluid.
 10. Themethod of claim 7 wherein the water-miscible organic liquid is presentin the fluid in an amount in the range of from about 40% to about 99% byweight of the fluid.
 11. A method comprising: providing an apparatuscomprising a tubing that comprises a first fluid located within a wellbore such that an annulus is formed between the tubing and a surface ofthe well bore; providing an aqueous-based insulating fluid thatcomprises an aqueous base fluid, a water-miscible organic liquid, and alayered silicate; and placing the aqueous-based insulating fluid in theannulus.
 12. The method of claim 11 wherein the aqueous-based insulatingfluid further comprises a polymer.
 13. The method of claim 11 whereinthe aqueous base fluid comprises at least one brine selected from thegroup consisting of: NaCl, NaBr, KCl, CaCl₂, CaBr₂, ZrBr₂, sodiumcarbonate, sodium formate, potassium formate, cesium formate, and aderivative thereof.
 14. The method of claim 11 wherein thewater-miscible organic liquid comprises at least one liquid selectedfrom the group consisting of: an ester, an amine, an alcohol, a polyol,a glycol ether, and a derivative thereof.
 15. The method of claim 14wherein the polyol comprises at least one polyol selected from the groupconsisting of: a water-soluble diol; ethylene glycol; propylene glycol;polyethylene glycol; polypropylene glycol; diethylene glycol;triethylene glycol; dipropylene glycol; tripropylene glycols a reactionproduct formed by reacting ethylene and propylene oxide with an activehydrogen base compound, a reaction product formed by reactingpolyethylene glycol and polypropylene glycol with an active hydrogenbase compound; neopentyl glycol; a pentanediol; a butanediol; anunsaturated diol; a butyne diol; a butene diol; a triol; glycerol; anethylene oxide adduct, a propylene oxide adduct; pentaerythritol; asugar alcohol; and any derivative thereof.
 16. The method of claim 11wherein the layered silicate comprises at least one layered silicateselected from the group consisting of: smectite, vermiculite, swellablefluoromica, montmorillonite, beidellite, hectorite, and saponite. 17.The method of claim 12 wherein the layered silicate is a syntheticlayered silicate.
 18. A method comprising: providing a first tubing thatcomprises at least a portion of a pipeline that contains a first fluid;providing a second tubing that substantially surrounds the first tubingthus creating an annulus between the first tubing and the second tubing;providing an aqueous-based insulating fluid that comprises an aqueousbase fluid, a water-miscible organic liquid, and a layered silicate; andplacing the aqueous-based insulating fluid in the annulus.
 19. Themethod of claim 18 wherein the aqueous-based insulating fluid furthercomprises a polymer.
 20. The method of claim 18 wherein the layeredsilicate comprises at least one layered silicate selected from the groupconsisting of: smectite, vermiculite, swellable fluoromica,montmorillonite, beidellite, hectorite, and saponite.
 21. The method ofclaim 18 wherein the water-miscible organic liquid comprises at leastone liquid selected from the group consisting of: an ester, an amine, analcohol, a polyol, a glycol ether, and a derivative thereof.
 22. Themethod of claim 21 wherein the polyol comprises at least one polyolselected from the group consisting of: a water-soluble diol; ethyleneglycol; propylene glycol; polyethylene glycol; polypropylene glycol;diethylene glycol; triethylene glycol; dipropylene glycol; tripropyleneglycol; a reaction product formed by reacting ethylene and propyleneoxide with an active hydrogen base compound; a reaction product formedby reacting polyethylene glycol and polypropylene glycol with an activehydrogen base compound; neopentyl glycol; a pentanediol; a butanediol;an unsaturated diol; a butyne diol; a butene diol; a triol; a glycerol;an ethylene oxide adduct; a propylene oxide adduct; pentaerythritol; asugar alcohol; and a derivative thereof.
 23. The method of claim 18wherein the layered silicate is present in the fluid in an amount in therange of from about 0.1% to about 15% by weight of the fluid and thewater-miscible organic liquid is present in the fluid in an amount inthe range of from about 40% to about 99% by weight of the fluid.
 24. Anaqueous-based insulating fluid comprising: an aqueous base fluid, awater-miscible organic liquid, and a layered silicate.